Compact Antenna with Artificial Magnetic Conductor for Noninvasive Continuous Blood Glucose Monitoring

A non-invasive technique for real-time continuous monitoring of blood glucose has been under development by Venkatarman’s research group in the ETA lab at RIT [16]-[18]. The methodology involves placing an antenna on the arm and monitoring changes in the resonant frequency, which is attributed to changes in the blood glucose level. This is because the blood’s permittivity depends on the glucose levels, and in turn, affects the antenna’s resonant frequency. In order to correlate the antenna’s resonant frequency shift with the real-time blood glucose change, glucose estimation was also modeled using the antenna’s input impedance. The antennas designed could successfully track the rise and fall of blood glucose using the glucose estimation model for both diabetic and non-diabetic patients. However, the antennas being used in this research are too large in size and not flexible. Additionally, the antenna’s radiation pattern was omnidirectional as it is a monopole antenna where the radiation is into the arm as well as away from the arm (back radiation). As a result, during the test procedure, the arm must be in a steady position throughout the time of the resonant frequency measurement. While it worked very well to prove the feasibility of continuous glucose monitoring, a better antenna is required for the next phase of research that involves clinical testing in a hospital environment. My goal in this thesis is to take the research further by designing antennas that are unidirectional, flexible and small in size. The unidirectional property can be achieved by using PEC (Perfect Electric Conductors) or PMC (Perfect Magnetic Conductors) over the antenna that can suppress the back radiation. Unlike the presence of infinite electric charges on an electric conductor, magnetic charges don’t exist. Therefore magnetic conductors are modeled artificially to achieve magnetic properties commonly known as Artificial Magnetic Conductors (AMC). The antenna used in this thesis is a monopole antenna with AMC as a ground plane. The advantage of using AMC over a perfect metal conductor as a ground plane to the antenna is that the AMC reflects the incident wave in phase and not out of phase like a regular metal conductor. Moreover, AMC layers not only suppresses the back radiation but also enhances the gain of the antenna into the arm. Using the AMC layer as the ground plane has also helped in miniaturizing the antenna. The different artificial magnetic conductors designed in this thesis are Rectangular Patch, Rectangular Ring, I-shaped, and Jerusalem Cross. The antennas were fabricated and tested in the unlicensed ISM band (2.4GHz – 2.5GHz) and are within the SAR standards laid out by FCC. The fabricated antenna was strapped to the arm and measurements of resonant frequency similar to those made previously were conducted with respect to time [16]-[18]. Two types of measurements were compared, that is, when the arm was held steady and when the arm had some movement. No significant change or fluctuations in the resonant frequency was observed with arm movement. Whereas the same type of measurements conducted on the monopole antenna in [18] showed significant fluctuations in the resonant frequency with arm movement. This experiment shows the significant advantage of the antenna with AMC layer as compared to the monopole antenna. Also demonstrated in the present work, is the ability of the designed antenna in tracking the increase and decrease of glucose level with changes in the resonant frequency, similar to [16]. This has been demonstrated with two non-diabetic subjects. Further, no back radiation was noted, when a hand above the setup is moved. Additionally, the effect of creeping waves was negligible. The antenna designed in this work will conform well to clinical studies of the ETA Lab research